Year	Percent
1970-01-01	5.9
1971-01-01	6.9
1972-01-01	6.6
1973-01-01	6.0
1974-01-01	6.7
1975-01-01	9.3
1976-01-01	8.6
1977-01-01	8.2
1978-01-01	7.2
1979-01-01	6.8
1980-01-01	7.4
1981-01-01	7.9
1982-01-01	9.4
1983-01-01	9.2
1984-01-01	7.6
1985-01-01	7.4
1986-01-01	7.1
1987-01-01	6.2
1988-01-01	5.6
1989-01-01	5.4
1990-01-01	5.5
1991-01-01	6.4
1992-01-01	7.0
1993-01-01	6.6
1994-01-01	6.0
1995-01-01	5.6
1996-01-01	5.4
1997-01-01	5.0
1998-01-01	4.6
1999-01-01	4.3
2000-01-01	4.1
2001-01-01	4.7
2002-01-01	5.6
2003-01-01	5.7
2004-01-01	5.4
2005-01-01	5.1
2006-01-01	4.6
2007-01-01	4.5
2008-01-01	5.4
2009-01-01	8.1
2010-01-01	8.6
2011-01-01	8.5
2012-01-01	7.9